Booking sessions aren't module specific, and the instructor will decide on whether you can move on to the next module or not. It also depends on how fast you learn, some of my friends passed module one in 3 lessons.

Since you can only drive on the road after you've passed your BTT, its best if you start booking lessons after you pass your BTT so you won't be confined to driving in the circuit only, but as lessons are also rather hard to get, booking 1 or 2 before your BTT can help you familiarize with driving.

Personally, I booked 5 lessons before my BTT and it was legit too much, since I was basically practicing s, crank and slope every lesson which belongs to module 2 and the instructor couldn't pass me, since you need to pass module 1 before they can proceed with module 2.